The present technology relates to an optical element. More specifically, the present technology relates to the shapes of lenses in an imaging lens unit and to an image pickup apparatus using the lenses.
Image pickup apparatuses using a solid-state image pickup device such as a CCD or CMOS sensor, for example, camera-equipped mobile telephones or digital still cameras, have been used. There has been a demand to reduce the size and thickness of such an image pickup apparatus and the size and length of an imaging lens included in the image pickup apparatus.
In recent years, compact image pickup apparatuses, such as camera-equipped mobile telephones, have been decreased in size and increased in number of pixels of an image pickup device. Models including a high-pixel-count image pickup device having a large number of pixels equivalent to those of a digital still camera have become popularized. Accordingly, the image pickup apparatus includes an imaging lens having high lens performance corresponding to such a high-pixel-count solid-state image pickup device.
Further, a ghost or flare is a factor in image degradation, and therefore, it is desirable to provide an imaging optical system that does not cause a ghost or flare. However, a ghost or flare has become more likely to occur with recent reduction in size and thickness, and is difficult to remove.
Accordingly, for example, Japanese Unexamined Patent Application Publication No. 2010-164755 proposes an optical element that suppresses the occurrence of a ghost or flare by providing an outer peripheral surface (edge surface) of a second lens with a non-parallel face that is not parallel to the optical axis.